Abstract:

An object of the present invention is to provide an atmosphere heat
treatment apparatus that is operable without relying on experiences
and/or intuitions of an operator, and a method of operating the same. The
atmosphere heat treatment apparatus includes an entrance side exhaust
path (26) for exhausting an inside atmosphere from an entrance side of a
carburizing chamber (10) to which a transforming gas is supplied, an exit
side exhaust path (35) for exhausting the inside atmosphere from an exit
side of the heat treatment chamber, and an opening degree adjusting lid
(28) attached for adjusting an opening degree of the entrance side
exhaust path (26), in which a part or whole of the exit side exhaust path
(35) is constituted of a pipe (46) having a predetermined inside
diameter. It is checked in advance a relationship of a supplying amount A
of the transforming gas with a ratio B:C of an exhaust amount B from the
exit side exhaust path (35) and an exhaust amount C from the entrance
side exhaust path (26) when a pressure in the carburizing chamber (10) is
adjusted to a predetermined furnace pressure by adjusting an opening
degree of the entrance side exhaust path (26) with the opening degree
adjusting lid (28), and when treating a work (W), the supplying amount A
of the transforming gas and a furnace pressure are adjusted so as to
control the ratio B:C of the exhaust amount B from the exit side exhaust
path (35) and the exhaust amount C from the entrance side exhaust path
(26) to be within a predetermined range.

Claims:

1. An atmosphere heat treatment apparatus, comprising:an entrance side
exhaust path for exhausting an inside atmosphere from an entrance side of
a heat treatment chamber to which a transforming gas is supplied;an exit
side exhaust path for exhausting the inside atmosphere from an exit side
of the heat treatment chamber; andan opening degree adjusting lid
attached for adjusting an opening degree of said entrance side exhaust
path,wherein a part or whole of said exit side exhaust path is
constituted of a pipe having a predetermined inside diameter.

2. The atmosphere heat treatment apparatus according to claim 1,wherein a
carry-in chamber for carrying in a work into the heat treatment chamber
is provided on the entrance side of the heat treatment chamber,
andwherein said entrance side exhaust path is provided in the carry-in
chamber.

3. The atmosphere heat treatment apparatus according to claim 1,wherein an
oil tank chamber for hardening a work is provided on the exit side of the
heat treatment chamber, andwherein said exit side exhaust path is
provided on the oil tank chamber.

4. The atmosphere heat treatment apparatus according to claim 1, further
comprising:an outside air intake path for taking in outside air; andan
opening/closing mechanism for opening/closing said outside air intake
path.

5. The atmosphere heat treatment apparatus according to claim 4,wherein an
oil tank chamber for hardening a work is provided on the exit side of the
heat treatment chamber, andwherein said outside air intake path is
provided on the oil tank chamber.

6. The atmosphere heat treatment apparatus according to claim 4,wherein an
entrance end of said exit side exhaust path is connected to said outside
air intake path between said opening/closing mechanism and an exit end of
said outside air intake path.

7. The atmosphere heat treatment apparatus according to claim 6, further
comprising a burner which consumes oxygen in the outside air taken in
from said outside air intake path for combustion,wherein said
opening/closing mechanism is provided between said burner and the exit
end of said outside air intake path, andwherein an exit end of said exit
side exhaust path is connected to said outside air intake path between
said burner and said opening/closing mechanism.

8. The atmosphere heat treatment apparatus according to claim 4,wherein
said exit side exhaust path is attached to said opening/closing
mechanism.

9. The atmosphere heat treatment apparatus according to claim 1, further
comprising a pilot burner for igniting the inside atmosphere exhausted by
said exit side exhaust path.

10. The atmosphere heat treatment apparatus according to claim 1, wherein
the heat treatment chamber is a carburizing chamber.

11. A method of operating an atmosphere heat treatment apparatus including
an entrance side exhaust path for exhausting an inside atmosphere from an
entrance side of a heat treatment chamber to which a transforming gas is
supplied, an exit side exhaust path for exhausting the inside atmosphere
from an exit side of the heat treatment chamber, and an opening degree
adjusting lid attached for adjusting an opening degree of the entrance
side exhaust path, wherein a part or whole of the exit side exhaust path
is constituted of a pipe having a predetermined inside diameter, the
method comprising:checking in advance a relationship of a supplying
amount A of the transforming gas with a ratio B:C of an exhaust amount B
from the exit side exhaust path and an exhaust amount C from the entrance
side exhaust path when a pressure in the heat treatment chamber is
adjusted to a predetermined furnace pressure by adjusting an opening
degree of the entrance side exhaust path with the opening degree
adjusting lid; andwhen treating a work, adjusting the supplying amount A
of the transforming gas and a furnace pressure so as to control the ratio
B:C of the exhaust amount B from the exit side exhaust path and the
exhaust amount C from the entrance side exhaust path to be within a
predetermined range.

12. The method of operating the atmosphere heat treatment apparatus
according to claim 11,wherein the atmosphere heat treatment apparatus
comprises an outside air intake path for taking in outside air,
andwherein when the outside air intake path is opened, oxygen in the
outside air is consumed for combustion, and then the outside air is taken
in via the outside air intake path.

13. The method of operating the atmosphere heat treatment apparatus
according to claim 12,wherein when outside air flows into the apparatus
through the exit side exhaust path when a pressure in the apparatus
becomes a negative pressure, oxygen in the outside air flowing into the
exit side exhaust path is consumed for combustion.

14. The method of operating the atmosphere heat treatment apparatus
according to claim 13,wherein oxygen in the outside air taken in from the
outside air intake path and oxygen in the outside air flowing in from the
exit side exhaust path are consumed for combustion by a same burner.

15. The method of operating the atmosphere heat treatment apparatus
according to claim 11, wherein the inside atmosphere exhausted by the
exit side exhaust path is ignited by a pilot burner.

16. The method of operating the atmosphere heat treatment apparatus
according to claim 11,wherein the heat treatment chamber is a carburizing
chamber.

Description:

TECHNICAL FIELD

[0001]The present invention relates to an atmosphere heat treatment
apparatus such as a sequential gas conditioning apparatus, which is used
for carburizing treatment of a work such as an automobile part, and a
method of operating the same.

BACKGROUND ART

[0002]There is known a sequential gas carburizing apparatus in which a
work such as an automobile part is carried through a carry-in chamber, a
carburizing chamber and an oil tank chamber in this order for performing
carburizing treatment thereon, and also the present applicant has
disclosed, for example, Japanese Patent Application Laid-open No.
H11-1759 (Patent Document 1).

[Patent Document 1]

[0003]Japanese Patent Application Laid-open No. H11-1759.

[0004]In such a sequential gas carburizing apparatus, in order to avoid
unevenness in carburization due to differences in positions of works in a
furnace, disturbance in furnace atmosphere due to flowing-in of the
outside air into the furnace, or risk of explosion or the like due to
flowing-in of the outside air, a transforming gas which is of
approximately five to ten times the furnace capacity per hour is supplied
into a carburizing chamber to thereby adjust the pressure in the
carburizing chamber to a predetermined furnace pressure. In this case,
for example, an entrance side exhaust path is provided in a carry-in
chamber connected to the entrance side of the carburizing chamber, and an
exit side exhaust path is provided in an oil tank chamber connected to
the exit side of the carburizing chamber, so as to supply the
transforming gas to the carburizing chamber. At the same time, the inside
atmosphere is exhausted from both the entrance side and the exit side of
the carburizing chamber, thereby burning the exhausted gas outside.

[0005]In the carburizing chamber, a preheating zone, a carburizing zone, a
diffusing zone, a hardening heating zone, and so on are provided in order
from the entrance side to the exit side, and among them, the hardening
heating zone is kept at a lower temperature compared to the other zones.
For example, in general, the preheating zone, the carburizing zone, the
diffusing zone are kept at approximately 930° C., whereas the
hardening heating zone is kept at approximately 850° C.

[0006]On the other hand, in the sequential gas carburizing apparatus, the
inside of the carburizing chamber is kept at a predetermined carbon
potential (CP) of 0.8% for example. However, the CP (carbon potential)
tends to increase when the temperature of the inside atmosphere drops,
and thus the CP increases when the inside atmosphere moves from the
carburizing zone or the diffusing zone kept at approximately 930°
C. to the hardening heating zone kept at approximately 850° C. for
example. For example, the CP of approximately 0.8% in the carburizing
zone or the diffusing zone which are kept at approximately 930° C.
increases to approximately 1.0% in the hardening heating zone which is
kept at approximately 850° C. Then, this increase of CP in the
hardening heating zone makes the carburizing treatment on works unable to
be controlled precisely.

[0007]Accordingly, the inside atmosphere of the entire carburizing chamber
is kept at a target value (0.8% for example) as much as possible by
exhausting the inside atmosphere of the carburizing chamber to the
entrance side of the carburizing chamber as much as possible, and thereby
making the exhaust amount to the exit side (hardening heating zone),
where the CP increases by temperature drop, of the carburizing chamber
relatively small. For example, by exhausting 70% to 80% of the inside
atmosphere in the carburizing chamber to the entrance side, and
exhausting the remaining 30% to 20% to the exit side, increase of the CP
in the hardening heating zone is suppressed effectively, which allows
keeping of the CP in the entire carburizing chamber almost at the target
value (0.8% for example) regardless of positions, and thus the
carburizing treatment becomes precisely controllable also during the
hardening heating.

[0008]For this purpose, conventionally, an operator appropriately adjusts
the opening degrees of the entrance side exhaust path and the exit side
exhaust path so as to allow exhausting of the inside atmosphere in the
carburizing chamber to the entrance side and the exit side by a
predetermined ratio (7:8 to 8:2). In this case, the operator sees for
example the size of flame or the like, which is exhausted to the outside
of the furnace and burnt, and adjusts the exhaust amount from the
entrance side exhaust path and the exhaust amount from the exit side
exhaust path, thereby controlling the inside atmosphere in the
carburizing chamber to be exhausted by the predetermined ratio to the
entrance side and the exit side.

[0009]However, such conventional control often relies on experiences
and/or intuitions of an operator, and thus objective judgment is not
possible. Also, since an experienced operator is required for operating
the apparatus, a human-related load becomes large, and hence reduction of
labor cannot be realized.

DISCLOSURE OF THE INVENTION

Problems to Be Solved by the Invention

[0010]Therefore, an object of the present invention is to provide an
atmosphere heat treatment apparatus that is operable without relying on
experiences and/or intuitions of an operator, and a method of operating
the same.

Means for Solving the Problems

[0011]According to the present invention, there is provided an atmosphere
heat treatment apparatus, which is characterized by including an entrance
side exhaust path for exhausting an inside atmosphere from an entrance
side of a heat treatment chamber to which a transforming gas is supplied,
an exit side exhaust path for exhausting the inside atmosphere from an
exit side of the heat treatment chamber, and an opening degree adjusting
lid attached for adjusting an opening degree of the entrance side exhaust
path, in which a part or whole of the exit side exhaust path is
constituted of a pipe having a predetermined inside diameter.

[0012]A carry-in chamber for carrying in a work into the heat treatment
chamber may be provided on the entrance side of the heat treatment
chamber chamber, and the entrance side exhaust path may be provided in
the carry-in chamber. Also, an oil tank chamber for hardening a work may
be provided on the exit side of the heat treatment chamber, and the exit
side exhaust path may be provided on the oil tank chamber.

[0013]Further, an outside air intake path for taking in outside air, and
an opening/closing mechanism for opening/closing the outside air intake
path may be included. Also, an oil tank chamber for hardening a work may
be provided on the exit side of the heat treatment chamber, and the
outside air intake path may be provided on the oil tank chamber. An
entrance end of the exit side exhaust path may be connected to the
outside air intake path between the opening/closing mechanism and an exit
end of the outside air intake path.

[0014]Also, a burner which consumes oxygen in the outside air taken in
from the outside air intake path for combustion may be included, and the
opening/closing mechanism may be provided between the burner and the exit
end of the outside air intake path. An exit end of the exit side exhaust
path may be connected to the outside air intake path between the burner
and the opening/closing mechanism.

[0015]The exit side exhaust path may be attached to the opening/closing
mechanism. A pilot burner for igniting the inside atmosphere exhausted by
the exit side exhaust path may be further included. The heat treatment
chamber may be a carburizing chamber.

[0016]Also, according to the present invention, there is provided a method
of operating an atmosphere heat treatment apparatus including an entrance
side exhaust path for exhausting an inside atmosphere from an entrance
side of a heat treatment chamber to which a transforming gas is supplied,
an exit side exhaust path for exhausting the inside atmosphere from an
exit side of the heat treatment chamber, and an opening degree adjusting
lid attached for adjusting an opening degree of the entrance side exhaust
path, in which a part or whole of the exit side exhaust path is
constituted of a pipe having a predetermined inside diameter, and the
method is characterized by including checking in advance a relationship
of a supplying amount A of the transforming gas with a ratio B:C of an
exhaust amount B from the exit side exhaust path and an exhaust amount C
from the entrance side exhaust path when a pressure in the heat treatment
chamber is adjusted to a predetermined furnace pressure by adjusting an
opening degree of the entrance side exhaust path with the opening degree
adjusting lid, and when treating a work, adjusting the supplying amount A
of the transforming gas and a furnace pressure so as to control the ratio
B:C of the exhaust amount B from the exit side exhaust path and the
exhaust amount C from the entrance side exhaust path to be within a
predetermined range.

[0017]The atmosphere heat treatment apparatus may include an outside air
intake path for taking in outside air, and when the outside air intake
path is opened, oxygen in the outside air may be consumed for combustion,
and then the outside air may be taken in via the outside air intake path.

[0018]Also, when outside air flows into the apparatus through the exit
side exhaust path when a pressure in the apparatus becomes a negative
pressure, oxygen in the outside air flowing into the exit side exhaust
path may be consumed for combustion. In this case, oxygen in the outside
air taken in from the outside air intake path and oxygen in the outside
air flowing in from the exit side exhaust path may be consumed for
combustion by a same burner.

[0019]The inside atmosphere exhausted by the exit side exhaust path may be
ignited by a pilot burner. The heat treatment chamber may be a
carburizing chamber.

EFFECT OF THE INVENTION

[0020]When a part or whole of the exit side exhaust path is constituted of
a pipe having a predetermined diameter, and a pressure in the heat
treatment chamber is adjusted to a constant furnace pressure, the amount
of gas exhausted from the exit side exhaust path becomes constant. Thus,
when the supply amount A of the transforming gas is increased and the
furnace pressure is made constant while a pressure in the heat treatment
chamber is kept at a desired furnace pressure, the amount of exhausted
gas from the exit side exhaust path is constant, which results in that
the amount of gas exhausted from the entrance side exhaust path is
increased by the amount of the increase of the supply amount A.
Accordingly, by checking in advance the pressure (furnace pressure) in
the heat treatment chamber, and the relationship of the supply amount A
of the transforming gas with the ratio B:C of the exhaust amount B from
the exit side exhaust path and the exhaust amount C from the entrance
side exhaust path, it becomes possible to treat a work in a predetermined
state. According to the present invention, it becomes possible to exhaust
the inside atmosphere of the heat treatment chamber to the entrance side
and the exit side by a desired ratio without relying on experiences or
intuitions of an operator. Accordingly, the CP of the entire heat
treatment chamber can be kept almost constant regardless of positions,
and hence the carburizing treatment can be controlled precisely. Also
according to the present invention, getting off of balance can be
determined by seeing an upper and lower limits of the furnace pressure as
long as jamming in the exit side exhaust path and the entrance side
exhaust path are prevented.

[0046]A graph showing a relationship of the supply amount A of a
transforming gas to the inside of a carburizing chamber with a ratio B:C
of the exhaust amount B from the exit side exhaust path and the exhaust
amount C from the entrance side exhaust path with a furnace pressure of 8
mmAq.

[0066]Hereinafter, preferred embodiments of the present invention will be
described with reference to the drawings, based on a sequential gas
carburizing apparatus as an example of an atmosphere heat treatment
apparatus. FIG. 1 is a schematic vertical cross-sectional view for
explaining a sequential gas carburizing apparatus 1 according to an
embodiment of the present invention. FIG. 2 is a vertical cross-sectional
view of an entrance side exhaust path 26. FIG. 3 is a vertical
cross-sectional view of an outside air intake path 35 having an exit side
exhaust path 36.

[0067]As shown in FIG. 1, the sequential gas carburizing apparatus 1 has a
carburizing chamber 10 as a heat treatment chamber, and a carry-in
chamber 11 for carrying a work W into the carburizing chamber 10 is
provided on an entrance side (left side of the carburizing chamber 10 in
FIG. 1) of the carburizing chamber 10, and an oil tank chamber 12 for oil
hardening the work W is provided on an exit side (right side of the
carburizing chamber 10 in FIG. 1) of the carburizing chamber. Inside the
carburizing chamber 10, a preheating zone 15, a carburizing zone 16, a
diffusing zone 17 and a hardening heating zone 18 are provided in order
from the entrance side to the exit side. Although not shown, not-shown
heaters are provided respectively in these preheating zone 15,
carburizing zone 16, diffusing zone 17 and hardening heating zone 18, and
the zones 15 to 18 can be heated to arbitrary atmospheric temperatures
respectively.

[0068]One side face of the carry-in chamber 11 (left side face of the
carry-in chamber 11 in FIG. 1) is constructed to be opened and closed by
a door 20. Similarly, one side face of the oil tank chamber 12 (right
side face of the oil tank chamber 12 in FIG. 1) is also constructed to be
opened and closed by a door 21. Further, a door 22 is provided between
the other side face of the oil tank chamber 12 (left side face of the oil
tank chamber 12 in FIG. 1) and the hardening heating zone 18, and the
door 22 opens and closes the hardening heating zone 18, and also opens
and closes the other side face of the oil tank chamber 12.

[0069]To an upper face of the carburizing chamber 10, there is connected a
gas supply path 25 for supplying a transforming gas produced in a
not-shown transforming furnace to the inside. Through this gas supply
path 25, an enrich gas can also be supplied to the inside of the
carburizing chamber 10.

[0070]On an upper face of the carry-in chamber 11, there is provided an
entrance side exhaust path 26 for exhausting the inside atmosphere from
the entrance side of the carburizing chamber 10. As shown in FIG. 2, the
entrance side exhaust path 26 has an entrance side exhaust path body 27
in a cylindrical shape, which is in communication with the inside of the
carry-in chamber 11, and the inside atmosphere of the carburizing chamber
10 is exhausted to the outside through this entrance side exhaust path
body 27. On an upper end of the entrance side exhaust path body 27, there
is attached an opening degree adjusting lid 28 for adjusting the opening
degree of the entrance side exhaust path 26 in an openable/closable
manner with a hinge 29. A tip portion of the opening degree adjusting lid
28 (end portion located opposite to a base end portion attached rotatably
on the upper end of the entrance side exhaust path body 27 via the hinge
29) is pushed up by a tip of a screw rod 30. The screw rod 30 is screwed
through a plate 31 attached on an outside of the upper end of the
entrance side exhaust path body 27, and by turning the screw rod 31, a
projecting amount of the tip of the screw rod 30 screwed through the
plate 31 changes, and accordingly, a pushed-up amount of the tip portion
of the opening degree adjusting lid 28 changes. When the projecting
amount of the tip of the screw rod 30 is increased by turning the screw
rod 30, the pushed-up amount of the tip portion of the opening degree
adjusting lid 28 increases, and the opening degree of the entrance side
exhaust path 26 (opening angle θ of the opening degree adjusting
lid 28) becomes large. Inversely, when the projecting amount of the tip
of the screw rod 30 is decreased by turning the screw rod 30, the
pushed-up amount of the tip portion of the opening degree adjusting lid
28 decreases, and the opening degree of the entrance side exhaust path 26
(opening angle θ of the opening degree adjusting lid 28) becomes
small.

[0071]In the vicinity of an upper end of the entrance side exhaust path
26, a burner 32 is arranged. Accordingly, the inside atmosphere exhausted
to the outside through the entrance side exhaust path 26 is ignited by
the burner 32 and burnt just after being exhausted.

[0072]As shown in FIG. 1, on an upper face of the oil tank chamber 12, an
outside air intake path 35 for taking outside air into the oil tank
chamber 12 is provided, and further an exit side exhaust path 36 for
exhausting the inside atmosphere from the exit side of the carburizing
chamber 10 is provided in a manner to branch from the outside air intake
path 35.

[0073]As shown in FIG. 3, the outside air intake path 35 has an outside
air intake path body 37 in a cylindrical shape, which is in communication
with the inside of the oil tank chamber 12, and on an upper side of the
outside air intake path body 37, there are formed a conical portion 38
which becomes wider upward, and a circumferential portion 39 following an
upper end of the conical portion 38. Inside the conical portion 38, a lid
40 is arranged, where normally the lid 40 is lowered by a not-shown
raising/lowering mechanism, and thereby the circumferential edge of the
lid 40 is in tight contact with an inside face of the conical portion 38
so as to close an upper end of the outside air intake path 35, as shown
by a solid line in FIG. 3. Thus, there is created a state such that the
outside air does not enter the inside of the oil tank chamber 12 via the
outside air intake path 35.

[0074]On the other hand, when the lid 40 is raised by the not-shown
raising/lowering mechanism, the circumferential edge of the lid 40 moves
away upward from the inside face of the conical portion 38, as shown by a
dashed line in FIG. 3, to open the upper end of the outside air intake
path 35. Thus, there is created a state that the outside air can enter
the inside of the oil tank chamber 12 via the outside air intake path 35.
Incidentally, in the state that the outside air can enter the inside of
the oil tank chamber 12 via the outside air intake path 35 in this
manner, a burner 41 arranged on the inside face of the circumferential
portion 39 ignites, and oxygen in the outside air entering the inside of
the oil tank chamber 12 from the outside air intake path 35 is consumed
for combustion of a flammable gas injected from the burner 41. Thus, the
outside air in a state that oxygen is removed therefrom enters the inside
of the oil tank chamber 12 from the outside air intake path 35.

[0075]The exit side exhaust path 36 provided so as to branch from the
outside air intake path 35 is constituted of an exit side exhaust path
base 45 in a cylindrical shape which is in communication with a side face
of the outside air intake path body 37, and a cylindrical pipe 46
connected to a tip of the exit side exhaust path base 45. The cylindrical
pipe 46 has a predetermined inside diameter L, and the opening area of
the cylindrical pipe 46 is set smaller than opening areas of the exit
side exhaust path base 45 and the outside air intake path body 37.

[0076]Normally, the upper end of the outside air intake path 35 is closed
by the lid 40, but via the exit side exhaust path 36 constituted of the
exit side exhaust path base 45 and the cylindrical pipe 46, the inside
atmosphere of the carburizing chamber 10 is exhausted to the outside also
from the exit side. However, with the cylindrical pipe 46 having the
predetermined inside diameter L, the amount of the inside atmosphere
exhausted from the exit side of the carburizing chamber 10 is restricted
in proportion to the inside diameter L.

[0077]In the vicinity of an upper end of the cylindrical pipe 46 arranged
vertically, a burner 50 is arranged. Thus, just after being exhausted,
the inside atmosphere exhausted to the outside from the exit side exhaust
path 36 is ignited and burnt by the burner 50.

[0078]Now, in the sequential gas carburizing apparatus 1 constructed as
above, a transforming gas is supplied to the inside of the carburizing
chamber 10 from the gas supply path 25. At the same time, the inside
atmosphere is exhausted from the entrance side of the carburizing chamber
10 through the entrance side exhaust path 26 provided on the carry-in
chamber 11, and also the inside atmosphere is exhausted from the exit
side of the carburizing chamber 10 through the outside air intake path 35
provided on the oil tank chamber 12. In this manner, while supplying the
transforming gas that is approximately five to ten times the furnace
capacity per hour to the inside of the carburizing chamber 10 from the
gas supply path 25, the inside atmosphere is exhausted from the entrance
side and the exit side of the carburizing chamber 10, thereby avoiding
unevenness in carburization due to differences in positions inside the
carburizing chamber 10 (positions in a furnace), disturbance in furnace
atmosphere due to flowing-in of outside air into the furnace, or risk of
explosion or the like due to flowing-in of the outside air. Note that the
inside atmospheres exhausted from the entrance side exhaust path 26 and
the outside air intake path 35 are ignited by the burners 32, 50
respectively and burnt just after being exhausted.

[0079]Here, on the entrance side exhaust path 26, the opening degree of
the entrance side exhaust path 26 (opening angle θ of the opening
degree adjusting lid 28) is adjusted by operating the screw rod 30, and
thereby the pressure inside the carburizing chamber 10 is adjusted to a
desired furnace pressure. Specifically, when the projecting amount of the
tip of the screw rod 30 is increased to increase the opening degree of
the entrance side exhaust path 26 (opening angle θ of the opening
degree adjusting lid 28), a resisting force applied when the inside
atmosphere of the carburizing chamber 10 is exhausted from the entrance
side exhaust path 26 is small, and thus the pressure inside the
carburizing chamber 10 becomes low. Inversely, when the projecting amount
of the tip of the screw rod 30 is decreased to reduce the opening degree
of the entrance side exhaust path 26 (opening angle θ of the
opening degree adjusting lid 28), the resisting force applied when the
inside atmosphere of the carburizing chamber 10 is exhausted from the
entrance side exhaust path 26 is large, and thus the pressure inside the
carburizing chamber 10 becomes high. Accordingly, by appropriately
adjusting the opening degree of the entrance side exhaust path 26
(opening angle θ of the opening degree adjusting lid 28), the
pressure inside the carburizing chamber 10 is adjusted to a desired
furnace pressure (positive pressure of approximately 5 mmAq to 10 mmAq
for example).

[0080]Also, while adjusting the pressure inside the carburizing chamber 10
to a desired furnace pressure in this manner, by adjusting a supply
amount (flow amount) A of the transforming gas supplied from the gas
supply path 25 to the inside of the carburizing chamber 10, the ratio B:C
of the exhaust amount B from the exit side exhaust path 35 and the
exhaust amount C from the entrance side exhaust path 26 is adjusted to be
within the range of 3:7 to 2:8 for example. In this case, the ratio B:C
of the exhaust amount B from the exit side exhaust path 35 and the
exhaust amount C from the entrance side exhaust path 26 can be adjusted
as follows.

[0081]Specifically, first, by adjusting the opening degree of the entrance
side exhaust path 26 by the angle θ of the opening degree adjusting
lid 28 as described above, the pressure inside the carburizing chamber 10
is adjusted to a desired furnace pressure. Then, while the pressure in
the carburizing chamber 10 is kept at the desired furnace pressure by
fixing the opening degree of the entrance side exhaust path 26, the
supply amount A of the transforming gas to the inside of the carburizing
chamber 10 is changed. On the other hand, there are checked a change in
the exhaust amount B from the exit side exhaust path along with the
change of the supply amount A of the transforming gas to the inside of
the carburizing chamber 10 in this manner as well as a change in the
exhaust amount (A-B) from the entrance side exhaust path. Then, there is
checked in advance a relationship of the supply amount A of the
transforming gas to the inside of the carburizing chamber 10 under the
desired furnace pressure (positive pressure of approximately 5 mmAq to 10
mmAq for example) with a ratio B:(A-B) of the exhaust amount B from the
outside air intake path 35 and the exhaust amount (A-B) from the entrance
side exhaust path 26.

[0082]Then, as will be described later, when the work W is actually
treated, according to a relationship checked thus in advance of the
supply amount A of the transforming gas to the inside of the carburizing
chamber 10 with a ratio B:C of the exhaust amount B form the exit side
exhaust path and the exhaust amount C from the entrance side exhaust
path, the supply amount (flow amount) A of the transforming gas supplied
to the inside of the carburizing chamber 10 from the gas supply path 25
and the furnace pressure are adjusted, so as to control the ratio B:C of
the exhaust amount B form the exit side exhaust path 35 and the exhaust
amount C from the entrance side exhaust path 26 to be within a desired
range (range of 3:7 to 2:8 for example). In this case, it is just needed
to adjust the supply amount A of the transforming gas according to a
predetermined relationship, it becomes possible to exhaust the inside
atmosphere of the carburizing chamber 10 to the entrance side and the
exit side by a desired ratio without relying on experiences and/or
intuitions of the operator.

[0083]Moreover, by heating with the not-shown heaters, the preheating zone
15, the carburizing zone 16, the diffusing zone 17 and the hardening
heating zone 18 are heated to arbitrary atmospheric temperatures
respectively, where for example, the preheating zone 15, the carburizing
zone 16 and the diffusing zone 17 are kept at an atmospheric temperature
of approximately 930° C., and the hardening heating zone 18 is
kept at an atmospheric temperature of approximately 930° C.

[0084]Here, as described above, while the transforming gas is supplied to
the inside of the carburizing chamber 10 from the gas supply path 25, the
inside atmosphere is exhausted both from the entrance side and the exit
side of the carburizing chamber 10 through the entrance side exhaust path
26 provided on the carry-in chamber 11 and the outside air intake path 35
provided on the oil tank chamber 12. However, the supply amount A of the
transforming gas is adjusted under the desired furnace pressure (positive
pressure of approximately 5 mmAq to 10 mmAq for example) so as to control
the ratio B:C of the exhaust amount B form the exit side exhaust path 35
and the exhaust amount C from the entrance side exhaust path 26 to be
within a desired range (range of 3:7 to 2:8 for example). Thus, the CP
hardly increases in the hardening heating zone 18 which has a lower
temperature as compared to the other zones 15 to 17, and thereby the CP
is kept at a desired value (0.8% for example) in all of the preheating
zone 15, the carburizing zone 16, the diffusing zone 17 and the hardening
heating zone 18.

[0085]While a carburizing atmosphere is formed inside the carburizing
chamber 10 in this manner, the door 20 is opened to carry a work W such
as an automobile part into the carry-in chamber 11, and the work W is
carried from the carry-in chamber 11 to the carburizing chamber 10. Then,
inside the carburizing chamber 10, the work W is carried sequentially
from the entrance side to the exit side, for being subjected to
respective treatments of preheating, carburizing, diffusing and hardening
sequentially in the preheating zone 15, the carburizing zone 16, the
diffusing zone 17 and the hardening heating zone 18. In this case, since
all the preheating zone 15, the carburizing zone 16, the diffusing zone
17 and the hardening heating zone 18 are kept at the desired CP (0.8% for
example) as described above, the carburizing treatment on the work W can
be controlled precisely.

[0086]Next, the door 22 is opened, and the work W subjected to the
carburizing treatment in the carburizing chamber 10 in this manner is
carried into the oil tank chamber 12 to be subjected to oil hardening.
Then, after the oil-hardening treatment is completed, the door 21 is
opened and the work W is carried out of the oil tank chamber 12.

[0087]When the door 21 is opened or when the door 22 is opened or closed
in this manner, a pressure inside the oil tank chamber 12 or the
carburizing chamber 10 may become a negative pressure temporarily. In
such a case, the lid 40 opens in the outside air intake path 35 explained
above with FIG. 3 to take in outside air to the inside of the oil tank
chamber 12 from the outside air intake path 35. At this time, by ignition
of the burner 41, the outside air in a state that oxygen is removed
therefrom enters the inside of the oil tank chamber 12, and thus the risk
of explosion or the like is avoided.

[0088]As above, an example of the preferred embodiment of the present
invention is shown, but it is needless to say that the present invention
is not limited to the embodiment explained here but may be changed and
implemented appropriately. In this embodiment, a structure is presented
in which the exit side exhaust path 36 is branched from the outside air
intake path 35, but these outside air intake path 35 and exit side
exhaust path 36 may be constructed separately. Also, the entire exit side
exhaust path 36 may be formed of the cylindrical pipe 46 having a
predetermined inside diameter L.

[0089]Before the carry-in chamber 11 or after the oil tank chamber 12 for
oil hardening, a purge chamber for purging a work W with an inert
(noncombustible) gas when the work W is carried in or out, and/or a
curtain burner may be provided. Also, inside the carburizing chamber 10,
a fan or the like may be provided other than the heaters. Also, carrying
of the work W inside the sequential gas carburizing apparatus 1 can be
performed appropriately with a roller house conveyor or a pusher.

[0090]Incidentally, with the above structures (structures of the outside
air intake path 35, the exit side exhaust path 36, and so on shown in
FIG. 3 for example), if the pressure inside the oil tank chamber 12 or
the carburizing chamber 10 becomes a negative pressure when the door 22
of the oil tank chamber 12 is opened when a work is moved from the
carburizing chamber 10 to the oil tank chamber 12 for example, it is
possible that the outside air flows in not only from the outside air
intake path 35 but also from the exit side exhaust path 36. In this case,
it is conceivable that a pilot burner 50 disposed at an exit end of the
exit side exhaust path 36 consumes oxygen in the outside air flowing in
from the exit side exhaust path 36 for combustion, and thus flowing in of
oxygen can be prevented. However, when it is desirable to prevent flowing
in of oxygen more effectively, an entrance end of the exit side exhaust
path 36 may be connected to a middle portion of the outside air intake
path 35, and the exit end of the exit side exhaust path 36 may be
connected between the burner 41 and the lid 40 of the opening/closing
mechanism 62 for example as shown in FIG. 4. In this manner, not only the
oxygen flowing in from the outside air intake path 35 but also the oxygen
flowing in from the exit side exhaust path 36 can be consumed for
combustion by the same burner 41. Therefore, flowing in of oxygen into
the oil tank chamber 12 and the carburizing chamber 10 can be prevented
more securely.

[0091]Similarly to the above-described outside air intake path 35 (refer
to FIG. 3), an outside air intake path 35 shown in FIG. 4 is constituted
of an outside air intake path body 37, a conical portion 38, and a
circumference portion 39, and has a structure to take in outside air into
the sequential gas carburizing apparatus 1 (oil tank chamber 12), and a
lid 40 and a burner 41 are arranged inside. Note that in this embodiment,
an opening/closing mechanism 62 for opening/closing the outside air
intake path 35 between the burner 41 and the carburizing chamber 10 has a
structure including the lid 40 and a not-shown raising/lowering mechanism
for raising/lowering the lid 40.

[0092]The burner 41 injects a combustible gas (hydrocarbon gas
(CmHn)) to the outside air taken in via the outside air intake
path 35. The burner 41 is a ring burner, curtain burner, or the like and
has a plurality of injection ports 41a to inject the combustible gas for
example. The injection ports 41a are disposed at the same height as each
other in a ring form arrangement so as to surround the center portion of
the circumferential portion 39. Specifically, it is a structure such that
the combustible gas is supplied from the entire circumference to the
outside air passing through the outside air intake path 35, so that the
outside air and the combustible gas can be mixed efficiently. Note that
the lid 40 of the opening/closing mechanism 62 is provided so as to
open/close the space between the burner 41 and an opening (upper end
portion opening of the circumferential portion 39) 35a that is an
entrance end when taking in the outside air via the outside air intake
path 35.

[0093]The exit side exhaust path 36 is constituted of an exit side exhaust
path base 45 in a cylindrical shape in communication with a side face of
the outside air intake path body 37, a cylindrical pipe 46 in a
substantially straight pipe shape connected to a tip of the exit side
exhaust path base 45, and a second exit side exhaust path base 67 in a
cylindrical shape which is connected to a tip of the cylindrical pipe 46
and in communication with a side face of the circumference portion 39.
Specifically, the exit side exhaust path 36 is branched from the outside
air intake path 35 and merged thereto on a side portion of the outside
air intake path 35, thereby becoming a detour (bypass) to bypass the lid
40. The opening 36a which is an entrance end of the exit side exhaust
path 36 when exhausting is connected to a middle portion of the outside
air intake path 35 between the lid 40 of the opening/closing mechanism 62
and an opening (lower end portion opening of the outside air intake path
body 37 connected to the oil tank chamber 12) 35b, which is an exit end
of the outside air intake path 35 when taking in the outside air. An
opening 36b which is an exit end of the exit side exhaust path 36 when
exhausting is connected to a middle portion of the outside air intake
path 35 between the burner 41 and the lid 40 of the opening/closing
mechanism 62.

[0094]The cylindrical pipe 46 has a predetermined inside diameter L, and
the opening area of the cylindrical pipe 46 is set smaller than opening
areas of the exit side exhaust path base 45, the second exit side exhaust
path base 67 and the outside air intake path body 37. Also, the
cylindrical pipe 46 is arranged on the outside of the outside air intake
path 35 in parallel to the outside air intake path 35.

[0095]In the vicinity of the opening 36b of the exit side exhaust path 36,
a pilot burner 70 for igniting the inside atmosphere exhausted by the
exit side exhaust path 36 is provided. This pilot burner 70 may be
arranged in the vicinity of an injection port 41a. For example, it may be
arranged between the opening 36b and the injection port 41a located on an
upper side of the opening 36b. In this manner, the pilot burner 70 can
also ignite the combustible gas injected from the injection port 41a. In
other words, the pilot burner 70 can also be used as a pilot burner for
igniting the burner 41.

[0096]In such a structure, when the outside air intake path 35 is closed
by the lid 40, the atmosphere in the oil tank chamber 12 flows into the
outside air intake path 35 from the oil tank chamber 12 through the
opening 35b, flows into the exit side exhaust path 36 between the opening
35b and the lid 40, further flows into the outside air intake path 35
from the exit side exhaust path 36 between the lid 40 and the burner 41,
and is exhausted to the outside of the sequential gas carburizing
apparatus 1 through the opening 35a of the outside air intake path 35.
Thus, exhaustion is performed through the opening 35b of the outside air
intake path 35, the exit side exhaust path 36, and the opening 35a.
Therefore, the inside atmosphere of the carburizing chamber 10 passes
through the oil tank chamber 12, the opening 35b of the outside air
intake path 35, the exit side exhaust path 36, and the opening 35a in
this order, and is exhausted to the outside of the sequential gas
carburizing apparatus 1. The amount of the inside atmosphere exhausted
from the exit side exhaust path 36 is restricted in proportion to the
inside diameter L.

[0097]Also, the inside atmosphere exhausted from the exit side exhaust
path 36 can be ignited and burnt by the pilot burner 70 just after being
exhausted. Specifically, combustible hydrocarbon gas (CH) and carbon
monoxide gas (CO) included in the inside atmosphere are burned in the
vicinity of the exits of the entrance side exhaust path 26 and the exit
side exhaust path 36 respectively, combined with oxygen (O2) in the
outside air and divided into carbon dioxide gas (CO2) and water
vapor (H2O), and released safely to the outside of the sequential
gas carburizing apparatus 1. Further, when the outside air intake path 35
is closed by the lid 40, the burner 41 is not needed to be ignited, and
thus it is preferable that the injection of combustible gas by the burner
41 is stopped. The pilot burner 50 may be operated constantly so that the
exhausted internal atmosphere is always ignited.

[0098]On the other hand, in a state that the outside air intake path 35 is
opened and the outside air can enter the inside of the oil tank chamber
12 when the pressure in the oil tank chamber 12 becomes a negative
pressure, the combustible gas is injected from the burner 41, and the
burner 41 is ignited by the pilot burner 70. Specifically, the oxygen
(O2) in the outside air taken in from the opening 35a of the outside
air intake path 35 is consumed for combustion of the combustible gas
injected by the burner 41, and thereby carbon dioxide (CO2) and
water (H2O) are generated. Thus, the outside air in a state that
oxygen is turned into carbon dioxide (CO2) and water (H2O) is
taken into the oil tank chamber 12 through the outside air intake path
35.

[0099]Also, when the pressure in the oil tank chamber 12 becomes a
negative pressure and the outside air is taken into the inside of the oil
tank chamber 12 from the outside air intake path 35 as described above,
the outside air flows into the oil tank chamber 12 at the same time also
from the exit side exhaust path 36, but this outside air flowing into the
exit side exhaust path 36 passes by the burner 41 in advance and is used
for combustion by the burner 41. Specifically, also in the outside air
flowing toward the oil tank chamber 12 via the exit side exhaust path 36,
oxygen in the outside air is consumed for combustion of the combustible
gas, and carbon dioxide and water vapor are produced. Thus, in a state
that oxygen is turned into carbon dioxide or water vapor, the outside air
enters the inside of the oil tank chamber 12 from the exit side exhaust
path 36.

[0100]Thus, by injecting the combustible gas from the burner 41 to the
outside air flowing in from the outside air intake path 35 and the
outside air flowing in from the exit side exhaust path 36 and burning the
combustible gas, oxygen in the outside air can be consumed for combustion
of the combustible gas and turned into a state of carbon dioxide and
water vapor before the outside air flows into the oil tank chamber 12 or
the carburizing chamber 10 via the outside air intake path 35 or the exit
side exhaust path 36. Therefore, increase of oxygen (O2)
concentration in the oil tank chamber 12 or the carburizing chamber 10
can be prevented securely, and the oil tank chamber 12 and the
carburizing chamber 10 can be maintained substantially in an oxygen-free
state therein. Specifically, oxygen in an active state which possibly
oxidizes a work can be reduced and turned into a state of carbon dioxide
that is inert and water vapor. Thus, oxidization of a work can be
prevented, and deterioration in quality of a work such as change of color
can be prevented effectively.

[0101]Also, for example, when the exit side exhaust path 36 is not
connected between the burner 41 and the lid 40 (for example, when the
exit side exhaust path base 67 is not provided, and the tip of the
cylindrical pipe 46 is open in the outside air (refer to FIG. 3)), it is
necessary, for securely consuming oxygen in the outside air flowing in
from the exit side exhaust path 36 for combustion, that the burner 41 is
provided separately on the exit side exhaust path 36. However, as shown
in FIG. 4, when the exit side exhaust path 36 is connected between the
burner 41 and the lid 40, it is no longer necessary to provide the burner
41 on the exit side exhaust path 36 separately. Specifically, it is
possible to consume the oxygen in the outside air taken in from the
outside air intake path 35 and the oxygen in the outside air flowing in
from the exit side exhaust path 36 for combustion by the same burner 41
provided on the outside air intake path 35. Therefore, it is possible to
decrease the equipment cost.

[0102]The above embodiment is constructed such that the opening 36a that
is the entrance end of the exit side exhaust path 36 is connected to a
middle portion of the outside air intake path 35, but the opening 36a may
be connected directly to the inside of the sequential gas carburizing
apparatus 1 (oil tank chamber 12). Specifically, it may be constructed
such that the inside atmosphere flows from the oil tank chamber 12 to the
exit side exhaust path 36 directly without intervention of the outside
air intake path 35. Also, the entire exit side exhaust path 36 may be
constructed by the cylindrical pipe having a predetermined diameter L.

[0103]In the above-described embodiments, the embodiments shown as
examples in FIG. 3 and FIG. 4 have a structure such that the exit side
exhaust path 36 is arranged outside the outside air intake path 35 and
the openings 36a, 36b are connected to the side portions of the outside
air intake path 35, but as shown in FIG. 5 for example, it is also
possible to arrange the exit side exhaust path 36 inside the outside air
intake path 35, and connect the openings 36a, 36b to the outside air
intake path 35 inside the outside air intake path 35. As shown in FIG. 5,
the exit side exhaust path 36 is constituted of a cylindrical pipe 80
attached to a lid 40. The cylindrical pipe 80 is a substantially straight
pipe having a predetermined inside diameter L', and is provided for
example so as to penetrate vertically a center portion of the lid 40
which is in a substantially circular shape in a plan view. A lower end
portion opening of the cylindrical pipe 80, specifically, an opening 36a
which is an entrance end of the exit side exhaust path 36 is provided
below the lid 40 between a lower face of the lid 40 and an opening 35b of
the outside air intake path 35. An upper end portion opening of the
cylindrical pipe 80, specifically, an opening 36b which is an exit end of
the exit side exhaust path 36 is provided between an upper face of the
lid 40 and a burner 41. In other words, this exit side exhaust path 36 is
branched from and merged to the outside air intake path 35 inside the
outside air intake path 35.

[0104]The cylindrical pipe 80 is moved to be raised/lowered integrally
with the lid 40 along with up/down movement of the lid 40 by driving of a
not-shown raising/lowering mechanism of the opening/closing mechanism 62.
In this manner, while the cylindrical pipe 80 is raised/lowered, the
opening 36a is always arranged between the lid 40 and the opening 35b,
and the opening 36b is always arranged between the lid 40 and the burner
41. Therefore, a space below the lid 40 and a space thereabove are
constantly in communication with each other via the exit side exhaust
path 36. Specifically, when the lid 40 is lowered and the outside air
intake path 35 is closed by the lid 40, the atmosphere inside the oil
tank chamber 12 can be exhausted through the opening 35b of the outside
air intake path 35, the exit side exhaust path 36, and the opening 35a.
The amount of the inside atmosphere to be exhausted is restricted in
proportion to the inside diameter L'. When the lid 40 is raised and the
outside air intake path 35 is opened, there is created a state such that
the outside air can be taken into the inside of the oil tank chamber 12
from the outside air intake path 35, and at the same time, the outside
air also flows from the exit side exhaust path 36 into the oil tank
chamber 12. However, the outside air flowing into this exit side exhaust
path 36 passes by the burner 41 in advance and used for combustion by the
burner 41. In this manner, also in such a structure, the outside air
passing through the exit side exhaust path 36 can flow into the oil tank
chamber 12 and the carburizing chamber 10 in a state that oxygen included
therein is consumed for combustion.

[0105]The above embodiments have a structure such that the outside air
intake path 35 is attached to the upper face of the oil tank chamber 12,
the outside air is made to flow in via a ceiling portion of the oil tank
chamber 12, and also the inside atmosphere is exhausted via the exit side
exhaust path 36 from the ceiling portion of the oil tank chamber 12.
However, the outside air intake path 35 may be attached to a side face of
the oil tank chamber 12. Specifically, it may be constructed such that
the outside air flows in via a side portion of the oil tank chamber 12,
and also the internal atmosphere is exhausted from a side portion of the
oil tank chamber 12 via the exit side exhaust path 36.

[0106]The burner 41 of the outside air intake path 35 may be provided as a
plurality of burners 41. For example, as shown in FIG. 6, two burners 41
may be provided in a vertical arrangement, and a plurality of injection
ports 41a may be provided as two vertical levels in a ring shape.
Further, the number of injection ports 41a injecting combustible gas may
be adjusted according to the pressure inside the oil tank chamber 12,
namely the flow amount of the outside air sucked into the oil tank
chamber 12. For example, when the flow amount of the outside air sucked
in is small, the combustible gas may be injected from only one of the two
burners 41, and when the flow amount of the outside air sucked in is
large, the combustible gas may be injected from the two burners 41
together.

[0107]In the above embodiments, as an atmosphere heat treatment apparatus,
the sequential gas carburizing apparatus 1 for performing a carburizing
treatment of a work W is shown as an example, but the present invention
can also be applied to various other atmosphere heat treatment
apparatuses performing heat treatment other than the carburizing
treatment. The atmosphere heat treatment apparatus may be a
carbonitriding apparatus performing carbonitriding treatment or a
nitriding apparatus performing nitriding treatment for example. Also, the
atmosphere heat treatment apparatus is not limited to an apparatus
performing a surface heat treatment of steel material, but may be an
apparatus performing a general heat treatment, such as a sequential gas
conditioning apparatus for performing conditioning. Specifically, the
atmosphere heat treatment apparatus may be an apparatus for performing
heat treatment such as annealing, hardening, tempering, or the like for
example. Also, the atmosphere heat treatment apparatus is not limited to
a sequential type heat treatment apparatus, but may be a batch-type heat
treatment apparatus.

[0108]The carburizing chamber 10 has a structure constituted of the
preheating zone 15, the carburizing zone 16, the diffusing zone 17 and
the hardening heating zone 18, but the structure inside the carburizing
chamber 10 is not limited to such a structure. Also, the carburizing
chamber 10 for performing carburizing is shown as an example of a heat
treatment chamber in the above-described embodiment, but the heat
treatment chamber can be changed appropriately according to the type of
an atmosphere heat treatment apparatus, and may be for example a
carbonitriding chamber, a nitriding chamber, a heat treatment chamber
performing conditioning, or the like.

EXAMPLE 1

[0109]In the cases that the inside diameter L (inside diameter L of the
cylindrical pipe) of the exit side exhaust path is 2/8B, 3/8B, 4/8B and
6/8B (B means an inch) in the sequential gas carburizing apparatus
explained in FIG. 1 and so on, and the exit side exhaust path is
constituted of each of the cylindrical pipes having the inside diameters
L, relationships of a supply amount A of a transforming gas to the inside
of the carburizing chamber with a ratio B:C of an exhaust amount B from
an exit side exhaust path and an exhaust amount C from the entrance side
exhaust path were checked.

[0110]First, the opening degree of the entrance side exhaust path was
adjusted, and the pressure (furnace pressure) in the carburizing chamber
was adjusted to 5 mmAq. Then, a relationship of the supply amount A with
the exhaust amount C from the entrance side exhaust path was checked in a
state that the furnace pressure is 5 mmAq, and results as shown in FIG. 8
were obtained. Also, a relationship of the supply amount A with the
exhaust amount B from the exit side exhaust path was checked, and results
as shown in FIG. 8 were obtained.

[0111]Next, the opening degree of the entrance side exhaust path was
adjusted, and the pressure (furnace pressure) in the carburizing chamber
was adjusted to 8 mmAq. Then, a relationship of the supply amount A with
the exhaust amount C from the entrance side exhaust path was checked in a
state that the furnace pressure is 8 mmAq, and results as shown in FIG. 9
were obtained. Also, a relationship of the supply amount A with the
exhaust amount B from the exit side exhaust path was checked, and results
as shown in FIG. 10 were obtained.

[0112]Further, the opening degree of the entrance side exhaust path was
adjusted, and the pressure (furnace pressure) in the carburizing chamber
was adjusted to 10 mmAq. Then, a relationship of the supply amount A with
the exhaust amount C from the entrance side exhaust path was checked in a
state that the furnace pressure is 10 mmAq, and results as shown in FIG.
11 were obtained. Also, a relationship of the supply amount A with the
exhaust amount B from the exit side exhaust path was checked, and results
as shown in FIG. 12 were obtained.

[0113]From these FIG. 7 to FIG. 12, the following facts were found.
Specifically, when the furnace pressure and the inside diameter L of the
exit side exhaust path are constant, the exhaust amount C from the
entrance side exhaust path is in proportion to the supply amount of the
transforming gas to the inside of the carburizing chamber. The exhaust
amount C of the entrance side exhaust path increases as the inside
diameter L of the exit side exhaust path decreases. The exhaust amount B
from the exit side exhaust path only depends on the furnace pressure and
the inside diameter L of the exit side exhaust path, and does not depend
on the supply amount A of the transforming gas to the inside of the
carburizing chamber. The exhaust amount B from the exit side exhaust path
increases along with increase of the furnace pressure. The exhaust amount
B from the exit side exhaust path increases as the inside diameter L
increases.

[0114]Also, a relationship of the supply amount A of the transforming gas
to the inside of the carburizing chamber with the ratio B:C of the
exhaust amount B from the exit side exhaust path and the exhaust amount C
from the entrance side exhaust path in a state that the furnace pressure
is 8 mmAq became as shown in FIG. 13. In FIG. 13, an appropriate range in
which the ratio B:C with the exhaust amount C becomes 3:7 to 2:8 was
exhibited (range in which B/A becomes 30% to 20%).

EXAMPLE 2

[0115]In the sequential gas carburizing apparatus 1 having the structure
in which the opening 36b that is the exit end of the exit side exhaust
path 36 is connected to the outside air intake path 35 between the burner
41 and the lid 40, a carburizing treatment on a work was performed. Then,
the oxygen concentration in the oil tank chamber 12 during the
carburizing treatment was measured, and the condition of the work after
the carburizing treatment was confirmed. As a result, the oxygen
(O2) concentration in the oil tank chamber 12 was suppressed to
approximately 0.4% to 0.5%. The work after the carburizing treatment had
less change in color, and was in a good condition.

COMPARATIVE EXAMPLE

[0116]In a sequential gas carburizing apparatus having a structure in
which the opening 36b that is the exit end of the exit side exhaust path
36 is not connected to the outside air intake path 35 but is made open to
the outside air, and other points are mostly the same as in the
above-described sequential gas carburizing apparatus 1, a carburizing
treatment on a work was performed. As a result, the oxygen concentration
in the oil tank chamber 12 was approximately 1.5% to 1.8%, which is
higher as compared to the above-described Example 1. On the work after
the carburizing treatment, there were black color changes on the entire
body.

INDUSTRIAL APPLICABILITY

[0117]The present invention can be used for carburizing treatment,
conditioning, or the like on a work such as an automobile part for
example.